1. Field of the Invention
The present invention relates to a vehicular antenna apparatus fitted to the inner surface (the cabin-side glass surface) of a window of a vehicle, such as a motor vehicle, and more specifically, it relates to a vehicular antenna apparatus including an electronic circuit unit that includes a preamplifier circuit and that is fitted to a glass surface provided with a radiating conductor.
2. Description of the Related Art
Hitherto, there has been known a vehicular antenna apparatus that includes a radiating conductor provided on the cabin-side glass surface of the rear window or the front window of a motor vehicle and an electronic circuit unit including a preamplifier circuit and fitted to the glass surface and that can thereby receive a circularly-polarized wave or a linearly-polarized wave transmitted from a satellite or an earth station. This type of antenna apparatus has a longer life and a lower risk of theft compared to antenna apparatuses installed outside the cabin, for example, on the roof, and has a more excellent space factor and a wider viewing angle compared to antenna apparatuses installed inside the cabin and near a window.
In this type of vehicular antenna apparatus, the electronic circuit unit fitted to a glass surface of a vehicle includes a circuit substrate having a preamplifier circuit, and a housing accommodating and holding the circuit substrate. The radiating conductor provided on the glass surface is electrically connected to the circuit substrate via a means, and thereby power feeding to the radiating conductor and loading of received signals can be performed. Hitherto, as an example of such an electrical connecting means, there has been known a structure in which a piece of conductor integral with the housing and protruding outward is soldered to a power feeding point of the radiating conductor, and thereby the radiating conductor on the glass surface and the preamplifier circuit of the circuit substrate are connected via the piece of conductor (see, for example, Japanese Unexamined Patent Application Publication No. 6-53722). In a vehicular antenna apparatus having such a structure, power feeding to the radiating conductor is performed via the piece of conductor protruding from the housing. Therefore, the piece of conductor is easily influenced by external noise, and it is difficult to secure necessary reliability. A vehicular antenna apparatus whose reliability is improved by using a coaxial feeder line, which is not easily influenced by external noise, as an electrical connecting means, and by soldering the feeder line to a power feeding point of the radiating conductor (see, for example, Japanese Unexamined Patent Application Publication No. 2006-13877).
In the conventional proposal disclosed in Japanese Unexamined Patent Application Publication No. 2006-13877, a radiating conductor provided on a glass surface of a vehicle and a circuit substrate in a housing are connected with a feeder line, and thereby a vehicular antenna apparatus that is not easily influenced by external noise is realized. However, in such a conventional proposal, at the end of assembling the antenna apparatus, it is necessary to solder one end of the feeder line to a power feeding point of the radiating conductor provided on the glass surface and to lay the feeder line along a predetermined pathway to a feeding terminal of the circuit substrate. These tasks need to be performed inside the cabin and are therefore inefficient. Therefore, the assembling cost is likely to be high. In addition, a slight error in the position at which the feeder line is soldered and connected to the radiating conductor causes impedance mismatching, and therefore it is difficult to obtain excellent antenna properties.